The invention relates to methods and devices for electro-photographic writing.
In widely used facsimile apparatuses, a light beam, typically delivered by a laser diode, is modulated by an input video signal and is focussed on a rotating photosensitive drum. The light beam generates, at each point of the drum, an electrostatic charge which represents the amount of received light. Dry toner in quantity proportioned to the deposited charges is transferred on the photosensitive drum. Then the dry toner is transferred on a paper sheet by an electrical field. The toner is fixed on the paper by pressing and heating it to a sufficient temperature.
The invention is particularly suitable for use in a facsimile apparatus for printing on regular paper. However it is also applicable to other systems and for instance to printers for connection with a personal or home computer.
In most electro-photographic devices using laser writing and thermal fixing, the thermal fixing means are continuously maintained at the required temperature for being immediately available at every instant. Heat generated by the fixing means should be exhausted to atmosphere for avoiding bringing other elements of the printer to an excessive temperature. For that purpose a blower is used and operates continuously, in stand-by conditions as well as in operating conditions. The sound level of the blower, which frequently exceeds 43 dB, is acceptable when the printer is in a noisy environment. On the other hand, it is not acceptable any longer for a desk top low-cost facsimile apparatus. Due to that sound level, facsimile apparatuses for that purpose have used thermal paper printers, in spite of the drawbacks of that substrate (high cost and difficulty of long term storage). A similar problem exists for a printer located close to a personal or home micro-computer.
It has also been proposed (U.S. Pat. No. 5,063,459 to Nakatani et al) to maintain the fixing device at a reduced temperature when a facsimile apparatus is in stand-by conditions, for reducing power consumption. However, that does not reduce the noise level associated with continuous operation of a heat removal blower.